I received error 721, which says the remote computer is not responding.

  • Cause: This issue can occur if the network firewall does not permit GRE traffic (IP protocol 47). PPTP uses GRE for tunneled data.
  • Solution: Configure the network firewall between the VPN client and the server to permit GRE. In addition, make sure that the network firewall permits TCP traffic on port 1723. Both of these conditions must be met to establish VPN connectivity by using PPTP. For more information, see article 888201, "You receive an "Error 721" error message when you try to establish a VPN connection through your Windows Server-based remote access server" in the Microsoft Knowledge Base.

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